Auto Racing: tires/wheels, willing crew, suspension clearance

Question
Hello, I race in a stock division on paved oval tracks. The rules state I must run a DOT 70 series tire. Due to suspension clearance issues I can't run anything taller than a 215/70-15 which is aprox. 7" wide. I also have 14" wheels and I am considering running a 195/70-14 which is aprox. 6" wide. Am I better off with more tread or less rotating mass and sidewall. I have many gear options so I can make either size work with that respect. Thanks Steve

Answer
Hi Steve.

Tread distortion may be the biggest issue here, The 7" wide tread is more  likely to curl up under side loads.  I'm afraid though, that your best answer is going to come from actual on track testing.  There are simply too darn many 'street' tires out there to make a recommendation. If you're buying new, go with the lowest tread wear rating, they will stick better.

Since you have plenty of gear options, I would suggest that you try the 14" tires first, They are going to have somewhat less sidewall to distort, and the narrower tread is less likely to curl. Even though they offer less static footprint, it may be that the REAL footprint under racing stresses is larger. And quite importantly, the rolling resistance will be lower, That can make a big difference.  

This is going to take some time on test days, rearrange the car so you can quickly change rear ends,  and take a willing crew with you. Get tires and wheels mounted and go testing.  The final set up should give you about 300 RPM over your horsepower peak at your lifting point on the straight.

Before you start too much testing though, take a walk through the pits and see what your competition is using. When you start to see a trend, you'll have a better idea of where to start. And finally  be sure you have your chassis set-up fairly well sorted.  To try and do a tire test with an evil car would be a waste of time and money.

Good luck

Dan Liddy
Sarasota, Florida